The microscopes have been conventionally used for analyses of cells and chromosomes in a variety of researches (e.g., cancer). In the analyses using the microscopes, however, it has cost a great deal of time and effort for acquiring the large amount of data and statistically examining the data. In most of the analyses of cells and chromosomes, the flow cytometers are now used for analyzing a lot of samples (i.e., cells and chromosomes) in a short period of time and acquiring highly-reliable statistical data. The flow cytometers are capable of forming a flow of sample liquid containing sample particles (e.g., cells with antibodies being fluorescent-stained), irradiating laser light to the sample liquid flow, and measuring fluorescence and scattered light emitted from each of the large amount of the flowing sample particles. Accordingly, the flow cytometers are capable of acquiring highly reliable statistical data. In general, the flow cytometers of the type are used for the medical field research.
Now, medical treatment using stem cells (also called regenerative cells) is highly expected in the future medical field. In the physiological process (e.g., propagation and differentiation) of cells forming a biological body, the stem cells have both of a self-reproduction ability and an ability to differentiate into a type of cells having specific functions. In other words, the stem cells have a copying ability to increase the number of them and an ability to change themselves into different cells. A variety of cells are classified into the stem cells. Examples are: embryonic stem cells (ES cells) to be taken out of embryos; adult stem cells to be taken out of adults; and fetal stem cells to be taken out of fetuses. If it is possible to differentiate the stem cells into a type of cells suitable for an organ damaged by injury or illness, for instance, it is possible to transplant the differentiated cells to the damaged portions for the reproduction of the damaged cells. Therefore, the stem cells are now actively studied in a variety of fields including the regenerative medical field.
For taking the stem cells out of the embryonic stem cells or the fetal stem cells, the embryos or fetuses are required to be destroyed (i.e., kill), which is an ethical problem. In response to this, the adult stem cells are used as research targets for some of the present regenerative medical research. This is because the stem cells are obtainable from living humans (children or adults) without damaging their bodies. Obviously, the adult stem cells are necessary for the research of the adult stem cells. The adult stem cells are generally found in the bone marrow and the blood, the cornea and the retina of the eye, the liver, the skin and the like. However, chances are quite low to actually find out the adult stem cells therein. Therefore, even if the large amount of sample cells are obtained, only the small amount of adult stem cells can be found. For example, the mesenchymal stem cells exist in the bone marrow stromal cells. The mesenchymal stem cells can differentiate into a variety of tissues (e.g., the bone, the cartilage, the fat, the muscle, the tendon and the nerve). Accordingly, the mesenchymal stem cells have been attracting attention of the regenerative medical field for reproduction of tissues lost by illness or external damage. However, the mesenchymal stem cells only exist in the bone marrow at the rate of one to hundred thousand. Therefore, for reproduction of the lost tissues, it is necessary to increase the number of tissues by temporarily taking the tissues out of the body and subsequently culturing the taken-out tissues on the outside of the body. To this end, it is necessary to separate and extract the small amount of stem cells from a plurality of cells in the bone marrow. Sort and collection systems (cell sorters), employing the aforementioned flow cytometers, are now used for separating and extracting the small amount of adult stem cells from the large amount of sample cells in a shorter time.
For example, “New Analysis and Separation Method for Stem Cells Using Ultra-High Speed Cell Sorter MoFlo™” discloses an example of the cell sorter of the type. FIG. 4 is a schematic configuration diagram for illustrating a cell sorter disclosed in “New Analysis and Separation Method for Stem Cells Using Ultra-High Speed Cell Sorter MoFlo™”. A cell sorter 100 is configured to discharge sample liquid which is ejected from a nozzle 103 as a jet flow 104. The sample liquid herein includes the large amount of sample cells 102. The large amount of sample cells 102 includes the small amount of stem cells. Therefore, the large amount of sample cells 102 is fluorescence-labeled for marking the stem cells. The cell sorter 100 irradiates measurement laser light 106 to the jet flow 104. In short, the cell sorter 100 is configured to sequentially irradiate the laser light 106 to the large amount of sample cells 102, respectively. Next, evaluation means (not illustrated in the figure), including photomultiplier tubes 108 and 110, obtains information of scattered light and fluorescence emitted from each of the large amount of sample cells 102. Then, the evaluation means (not illustrated in the figure) determines whether or not each of the sample cells, irradiated with the laser light 106, is among the stem cells (note a group of the sample cells, including a lot of stem cells, is specified in “New Analysis and Separation Method for Stem Cells Using Ultra-High Speed Cell Sorter MoFlo™”). The flow cytometers are generally configured as described above. However, the cell sorter 100 has a function of separating (i.e., sorting) the specified cells. For example, the cell sorter 100 is configured to vibrate the nozzle 103 at high frequency using a piezoelectric element (not illustrated in the figure). Accordingly, the jet flow 104 is forcibly changed into droplets 112. At the moment when a specific sample cell (e.g., a sample stem cell) enters a droplet 112 during forming the droplet 112, the droplet 112, including the specific sample cell, is positively (+) or negatively (−) charged (note the figure shows a positively-charged example).
The droplets 112 sequentially pass through a horizontal electric field 118 formed by two electric-field formation plate electrodes 114 and 116. In this case, only the falling direction of the charged droplets 112 is changed (i.e., deflected) by the horizontal electric field. Accordingly, the fallen droplets 112 are collected by a desired test tube 120. Thus, only the specific sample cells 102 (e.g., sample stem cells) are collected by the test tube 120. On the other hand, the other non-charged sample cells 102 fall in the vertical direction, and are accordingly collected by a waste liquid receiver 122.